Additional resources about Channel
effects

Satya Meka provides the Separate RGB effect plug-in on the After Effects Scripts website. This effect—which was written with Pixel Bender—offsets, scales, and rotates each color channel of an image separately.

Chris Forrester provides a video tutorial on his website that shows how to use the Channel Mixer, Shift Channels, and Set Matte effects to create mattes from color ID passes from 3D applications. The tutorial also provides an animation preset that sets up the parameters in the Channel Mixer effect for the use of an RGBCMY color ID pass.

Arithmetic effect

The Arithmetic effect performs various simple mathematical
operations on the red, green, and blue channels of an image.

This effect works with 8-bpc color.

Operator

The operation to perform between the value you specify for
each channel and the existing value of that channel for each pixel
in the image:

And, Or, and Xor

Apply bitwise logical operations.

Add, Subtract, Multiply, and Difference

Apply basic math functions.

Max

Set the channel value of the pixel to the greater of the
specified value and the original value of the pixel.

Min

Set the channel value of the pixel to the lesser of the specified
value and the original value of the pixel.

Block Above

Set the channel value of the pixel to zero if the original
value of the pixel is greater than the value specified; otherwise,
leave the original value.

Block Below

Set the channel value of the pixel to zero if the original
value of the pixel is less than the value specified; otherwise,
leave the original value.

Slice

Set the channel value of the pixel to 1.0 if the original
value of the pixel is above the specified value; otherwise, set
the value to zero. In both cases, the values for the other color
channels are set to 1.0.

Screen

Multiplies the complements of the channel values, and then
takes the complement of the result. The result color is never darker
than either input color.

Clip Result Values

Prevents all functions from creating color values that exceed the
valid range. If this option isn’t selected, some color values may
wrap around.

Blend effect

The Blend effect blends two layers using one of five modes.

You can blend layers more easily and quickly using blending modes, but you can’t animate blending modes. The advantage of using the Blend effect is that you can animate it. (See Blending modes and layer styles.)

Color Only colorizes each pixel in the original image based on the color of each corresponding pixel in the secondary image.

Tint Only is similar to Color Only but tints pixels in the original image only if they’re already colored.

Darken Only darkens each pixel in the original image that is lighter than the corresponding pixel in the secondary image.

Lighten Only lightens each pixel in the original image that is darker than the corresponding pixel in the secondary image.

Crossfade causes the original image to fade out while the secondary image fades in.

ملاحظة:

You can create a crossfade without applying an effect by animating the Opacity property of one layer on top of another. However, this technique doesn’t work if the frontmost layer has any transparent portions (which allow the other layer to show through, even when at full opacity). The Crossfade mode creates a proper crossfade between two layers, even if both have transparent regions.

Blend With Original

The transparency of the effect. The result of the effect
is blended with the original image, with the effect result composited
on top. The higher you set this value, the less the effect affects
the layer. For example, if you set this value to 100%, the effect
has no visible result on the layer; if you set this value to 0%,
the original image doesn’t show through.

If Layer Sizes Differ

Specifies how to position the control layer. The quality setting
of the layer affects Blend only if Stretch To Fit is selected and
if the layers are of different sizes. Stretching at Best quality
is much smoother.

Calculations effect

The Calculations effect combines channels of one layer
with the channels of a second layer.

This effect works with 8-bpc and 16-bpc color.

Input Channel

The channel to extract and use as input to the blending operation.
RGBA displays all channels normally. Gray converts all color channel values
for a pixel to the luminance value of the original pixel. Red, Green,
or Blue converts all color channel values for a pixel to the value
of the selected color channel for the original pixel. Alpha converts
all channels to the value of the alpha channel for the original
pixel.

Invert Input

Inverts the layer (subtracts each channel value from 1.0)
before the effect extracts the specified channel information.

Second Layer

The control layer with which Calculations blends the original layer.

Second Layer Channel

The channel to be blended with the input channels.

Second Layer Opacity

The opacity of the second layer. Use a setting of 0% for the
second layer to have no influence on the output.

Invert Second Layer

Inverts the second layer (subtracts each channel value from
1.0) before the effect extracts the specified channel information.

Stretch Second Layer To Fit

Stretches the second layer to the dimensions of the original
layer before blending. Deselect to center the second layer on the original
layer.

Preserve Transparency

Ensures that the alpha channel of the original layer isn’t modified.

Channel Combiner effect

The Channel Combiner effect extracts, displays, and adjusts channel values for a layer.

ملاحظة:

You can use this effect to view any channel as a grayscale image by choosing the channel from the From menu and choosing Lightness Only from the To menu.

This effect works with 8-bpc color.

Use 2nd Layer

Retrieve values from Source Layer, which can be any layer
in the composition.

From

Which values to use as input; the first several items in
the menu are multichannel combinations of input and output options,
so they don’t require you to set a To value.

Saturation
Multiplied uses the saturation value multiplied by the lightness value,
where lightness is the minimum distance to black or white. For example, a
dark or light blue pixel has a lower value than a bright or pure blue
pixel. This option represents the most common view of the saturation
value of a pixel.

The channels to which to apply the values. Choose Red Only,
Green Only, and Blue Only to apply the value to one channel only
and set the other color channels to zero. Choose Alpha Only to apply
the value to the alpha channel and set the color channels to 1.0.
When you select Hue Only, the applied hue value is combined with
50% lightness and 100% saturation. When you select Lightness Only,
the applied lightness value is combined with 0% saturation, which
then gives the hue no influence. When you select Saturation Only,
the applied saturation values are combined with 0% hue and 50% lightness.

Compound Arithmetic effect

The Compound Arithmetic effect mathematically combines
the layer to which it is applied with a control layer. The Compound
Arithmetic effect is intended only to provide compatibility with
projects created in earlier versions of After Effects that use the
Compound Arithmetic effect. Using blending modes is usually more effective
than using the Compound Arithmetic effect.

This effect works with 8-bpc color.

Second Source Layer

The layer to use with the current layer in the given operation.

Operator

The operation to perform between the two layers.

Operate On Channels

The channels to which the effect is applied.

Overflow Behavior

How the effect remaps values that fall outside the grayscale range
of 0-255.

Clip

Values above 255 are mapped to 255. Values below 0 are mapped
to 0.

Wrap

Values above 255 and below 0 are wrapped back around into
the 0-255 range. For example, a value of 258 wraps around to 2,
a value of 256 wraps around to 0, and a value of ‑3 wraps around
to 253.

Scale

The maximum and minimum values are remapped to 255 and 0,
and intermediate values are stretched or compressed to fit within
this range.

Stretch Second Source To Fit

Scales the second layer to match the size (width and height)
of the current layer. If this option is deselected, the second layer
is placed at the current size of its source, aligned with the upper
left corner of the source layer.

Blend With Original

The transparency of the effect. The result of the effect
is blended with the original image, with the effect result composited
on top. The higher you set this value, the less the effect affects
the layer. For example, if you set this value to 100%, the effect
has no visible result on the layer; if you set this value to 0%,
the original image doesn’t show through.

Invert effect

The Invert effect inverts the color information of an image.

This effect works with 8-bpc, 16-bpc, and 32-bpc color.

Original (left), and with effect applied (right)

Channel

Which channel or channels to invert. Each group of items
operates in a particular color space, inverting either the entire
image in that color space or only a single channel.

RGB/Red/Green/Blue

RGB inverts all three of the additive color channels. Red, Green,
and Blue each invert an individual color channel.

HLS/Hue/Lightness/Saturation

HLS inverts all three of the calculated color channels. Hue,
Lightness, and Saturation each invert an individual color channel.

YIQ/Luminance/In Phase Chrominance/Quadrature Chrominance

YIQ inverts all three NTSC luminance and chrominance channels.
Y (luminance), I (in‑phase chrominance), and Q (quadrature chrominance)
each invert an individual channel.

Alpha

Inverts the alpha channel of the image. The alpha channel
isn’t a color channel; it specifies transparency.

Blend With Original

The transparency of the effect. The result of the effect
is blended with the original image, with the effect result composited
on top. The higher you set this value, the less the effect affects
the layer. For example, if you set this value to 100%, the effect
has no visible result on the layer; if you set this value to 0%,
the original image doesn’t show through.

The Invert effect uses GPU acceleration for faster rendering.

Minimax effect

The Minimax effect assigns each channel of a pixel the
minimum or maximum value for that channel found within a specified
radius.

This effect can be used to enlarge or reduce a matte. For example,
a white solid area surrounded by black shrinks one pixel on each
side using Minimum and a radius of 1.

The quality setting of the layer doesn’t affect Minimax.

This effect works with 8-bpc and 16-bpc color.

Operation

Minimum assigns each channel of a pixel the minimum value
for the specified channel within the specified radius. Maximum assigns
each channel of a pixel the maximum value. Minimum Then Maximum
performs the Minimum operation and then the Maximum operation. Maximum
Then Minimum performs the Maximum operation and then the Minimum
operation.

Direction

The axis along which to scan for values. Horizontal &
Vertical scans all directions.

Remove Color Matting effect

The Remove Color Matting effect removes color fringes (halos) from layers with premultiplied color channels. Halos often occur when an area of partial transparency retains the color of the original background and is composited into a context with a different background color. Use this effect along with effects that create transparency—such as keying effects—to achieve more control over the appearance of areas of partial transparency. (See Alpha channel interpretation: premultiplied or straight.)

This effect works with 8-bpc, 16-bpc, and 32-bpc color.

Original (left), and with Remove Color Matting effect applied
(right)

Use Background Color to specify the new background color. To allow this effect to generate color values outside the range 0.0-1.0 when working in 32-bpc color, deselect Clip HDR Values.

The Remove Color Matting effect was previously known as the Unmultiply effect. The old name refers to the fact that this effect functions by unpremultiplying color channels—removing the result of the background color being premultiplied with the color channels of the layer in areas of partial transparency. This functionality differs from Knoll Unmult and other effects that synthesize an alpha channel from the color channels in an image.

Todd Kopriva provides a post on the Adobe website that describes the use of the Remove Color Matting and Shift Channels effects to remove black backgrounds from images.

Set Channels effect

The Set Channels effect copies channels from control
layers (source layers) to the red, green, blue, and alpha channels
of the effect layer. For example, you can take the luminance values
of the pixels of a control layer and use them as the blue values
for the pixels of the effect layer.

This effect works with 8-bpc and 16-bpc color.

Set Matte effect

The Set Matte effect replaces the alpha channel (matte)
of a layer with a channel from another layer above it for the creation
of traveling matte results. The Set Matte effect is intended only
to provide compatibility with projects created in earlier versions
of After Effects that use the Set Matte effect.

This effect works with 8-bpc and 16-bpc color. In After Effects
CS6 or later, this effect works in 32-bit color.

Original (upper-left), matte layer (lower-left), and result
(lower-right)

Sometimes, it’s easier and faster to create traveling mattes
by using a track matte instead of using the Set Matte effect. However,
using the Set Matte effect provides some advantages over defining
a layer as a track matte layer. The layer used as the matte with
the Set Matte effect can be anywhere in the layer stacking order,
unlike a track matte layer, which must be directly above the matted
layer in the layer stacking order. Also, one layer can be used as
the matte for multiple layers with the Set Matte effect. (See Track
mattes and traveling mattes.)

Take Matte From Layer

The layer to use as the replacement matte.

Use For Matte

The channel to use for the matte.

Invert Matte

Inverts the transparency values of the matte.

Stretch Matte To Fit

Scales the selected layer to match the size of the current layer.
If Stretch Matte To Fit is deselected, the layer designated as the
matte is centered in the first layer.

Composite Matte With Original

Composites the new matte with the current layer, rather than
replacing it. The resulting matte allows the image to show through
only where the current matte and the new matte both have some opacity.

Premultiply Matte Layer

Premultiplies the new matte layer with the current layer.

Shift Channels effect

The Shift Channels effect replaces red, green, blue,
and alpha channels in the image with values from other channels.

This effect works with 8-bpc, 16-bpc, and 32-bpc color.

Take Channel From

The channel to use as a source.

Todd Kopriva provides a post on the Adobe website that describes the use
of the Remove Color Matting and Shift Channels effects to remove
black backgrounds from images.

Solid Composite effect

The Solid Composite effect offers a quick way to create
a composite of a new color solid behind the original source layer.